Viscoelastic properties of dilute macromolecular solutions can provide information about molecular size and shape and an unambiguous test of flexibility. The Birnboim-Schrag multiple-lumped resonator will be used to study rigid or semiflexible rodlike molecules such as minifilaments of myosin and myosin rod, soluble collagen, xanthan polysaccharide, and schizophyllan polysaccharide. From the frequency dependence of the storage and loss shear moduli, the rotational relaxation time can be determined, as well as (if flexibility exists) the persistence length and micro-Young's modulus. Dynamic light scattering measurements may provide self-diffusion coefficients of macromolecules of various shapes in concentrated solutions and also in different environments such as concentrated solutions of another macromolecular species or gels. Mechanical properties of fibrin clots will be studied in small deformations and also in large deformations where changes in structure can be monitored by superposed small oscillating deformations during creep or stress relaxation. Birefringence will also be measured. These measurements provide information about the enhancement of structure at large strains, structural rearrangements and damage, and structural healing. Special attention will be given to clots from fibrinogen which retains its B peptides as well as that from which the Alpha appendages have been removed. Fibrin films made from such clots by removal of fluid to concentrate the system in one direction will be studied in stress relaxation. Gels, and films made from these gels, of other proteins such as gelatin and denatured bovine plasma albumin will be investigated by similar techniques, as well as, possibly, by high voltage electron microscopy and small-angle X-ray scattering.